1. Field of the Invention
The invention relates to marking apparatus used in a process for producing multi-layered printed circuit board.
2. Related Art
As electric products are becoming lighter, thinner, shorter, smaller and more functional, which is typically shown in cellular phones, a printed circuit board used in such electric products is also becoming more precise. The multi layered printed circuit board has been developed in this trend, the board is manufactured by a so-called build-up method. The multi layered printed circuit board has a core board, on both back and front faces of which resin isolation layers and conductive patterns made of copper or the like are alternately formed and laminated. The layers are conductive through a hole called a via hole that is plated by copper. The conductive patterns are formed by a lithography method using an aligner having a photo mask that is depicted with an original pattern.
When building up the layers, it is very important to adjust the positions of the layers. The new pattern on a new build up layer must be precisely formed at a certain position relevant to the old pattern on the old layer formed already. To accomplish the alignment between the new and old patterns, an alignment mark depicted on the film mask and a board mark (referred to as a standard mark hereinafter) formed on the board are utilized.
Furthermore, the position of the via hole must be precisely determined in relation to the unseen pattern formed on a lower layer.
However, the alignment mark on the core board is invisible because the layer is covered by copper foil before the pattern is formed.
In the prior art, the portion on the build up layer corresponding to on the standard mark on the core board is masked before coating the whole surface of the build up layer with a copper foil and the mask is tore off after the coating in order to avoid covering the portion with the foil.
Further, a hole mark formed through the board is often employed instead of the alignment mark. However, this method needs the troublesome treatment to prevent resin for forming an insulation layer entering into the hole or to remove adhered resin in the hole when forming the insulation layer.
The invention will resolve the problems in the conventional technology described above. Its objective is to provide a marking apparatus that will, by detecting the standard mark by X-ray scanning, allow new alignment marks to be formed on the subsequent outer layers of a multi-layered printed circuit board in relation to the standard mark.
A marking apparatus of the invention used in a process for producing multi-layered printed circuit boards with a plurality of insulation layers and patterned conductive layers is characterized in having a mark that can be detected by X-rays formed on at least one of said layers of said multi-layered printed circuit board, means for irradiating X-rays on an area containing said mark and detecting the position of the mark, and means for making another mark on an outer layer of said multi-layered printed circuit board.
In said construction, since another alignment mark can be formed on the subsequent outer layers based on the detected mark, it becomes possible to align the news marks to the standard mark. The new alignment mark(s) is typically formed at the position on each layer, corresponding precisely to the detected position of the mark.
The new alignment mark is generally formed on the next conductive layer to be built up, or on the resist used for patterning the conductive layer. In case the dry film resist is used, it is preferred to develop the color of the resist before forming the new alignment mark.
It is further preferred to compose the detection means described above in such order as projecting the X-rayed mark in the multi-layered printed circuit board on a fluorescence screen, thereby making the image of the mark visible, and then photographing the mark by CCD camera to determine its position. Such art has been disclosed by the present assignee in the U.S. application Ser. No.: 09/804,217.